When making a collapsible ski pole or trekking pole with the goal of minimum size possible in the collapsed mode, one solution is to have multiple telescopic shafts that slide inside each other completely. A design challenge is determining how to secure the individual shafts rigidly in both directions when the pole assembly is in the extended mode.
The shaft sections may be secured in the extended mode with a locking pin that extends through overlapping inner and outer shafts. There are two main locking pins designs for securing shafts in both directions (both directions meaning extending or collapsing).
Referring to FIGS. 1A and 1B, the first design is the “pin through the outer shaft design.” The outer shaft on top includes a series of holes, and the inner shaft below includes a spring pin that is receivable within one of the holes. As shown in FIG. 1B, the inner shaft is received within the outer shaft, and the spring pin is disposed in one of the holes in the outer shaft. This design substantially secures the shafts rigidly in both directions.
One major issue with this prior art pin through the outer shaft design is that it requires that the shafts have some sort of non-round cross-sectional shape so the shafts cannot spin or rotate with respect to each other. If the shafts are instead round in cross-section, the orientation of the outer and inner shafts and holes will not stay aligned, and it is very difficult to find the correct location for the spring pin to push thru the outer shaft hole. A prior attempt to remedy this issue is to paint a longitudinal line on the inner shaft aligned with the spring pin. This way the user can attempt to align the shafts by sight using the guide line. This solution works but is not easy or quick to use.
The second issue with this prior art pin through the outer shaft design is that the two shafts are held together by only the pin, and the slop or play in the system is based on the diameter difference between the pin and the holes. There is a small amount of play required to allow the pin to pop thru the holes easily; and therefore, this system can have rattle issues.
Referring to FIG. 1C, the second design is the “pin below outer shaft design.” This design includes an upper/outer shaft and a lower/inner shaft. The spring pin in the lower/inner shaft has popped out below the upper/outer shaft and therefore does not allow the upper shaft to slide down over the inner shaft when downward force is put on the pole. This design addresses the major issue with the above-described method of aligning a pin with a hole, as the pin just pops out below the upper/outer shaft, and no orientation is needed. However, the issue with this pin below outer shaft design is that nothing is holding the lower/inner shaft from upwardly extending further and even falling out of the upper/outer shaft.
Prior solutions to this issue have included using an internal cord, string or cable to hold the two shafts together and to prevent them from extending too far apart. However, with this cord solution, the cord must be either fixed in length or it must be made taut after each extension of the pole. If the cord is fixed in length, the expansion of the two shafts will be limited and defined by the length of the cord. If the cord is adjustable in length, the cord is loosened to allow the pole to be freely extended, and then once extended the cord is tightened to assure the spring pin is held firmly against the lower edge of the upper/outer shaft. When held tightly against the lower edge of the upper/outer shaft, there is substantially no rattling or play in the pole assembly and the pole will not overextend. However, loosening and tightening the cord with each extension or collapse of the pole assembly is very cumbersome and time consuming.
Another limitation of the adjustable cord solution is that it can only be adequately used between the expansion of two shafts. For instance, in a three-piece collapsible pole assembly having a first shaft with second and third shafts telescopingly received on the first shaft, the cord would extend between the first, second, and third shafts. The cord may not prevent one of the second and third shafts from extending beyond their expansion range before being stopped by the cord unless the second and third shafts were slowly extended simultaneously.
Thus, it can be appreciated that there is a need for an improved collapsible ski or trekking pole assembly that improves upon at least these above-described prior art designs.